I'm thinking about starting judo I've been training jiu Jitsu for a while and a weak point in my game is takedowns and wanna learn judo so I could do some takedowns and slams, any advice would be appreciated, thanks! 
My advice is to find a school that focuses on competitive judo. And learn judo for sake of learning judo because it does take time. Very few BJJ players transition to judo well. I have only seen one in the past 5-10 years. The rest do it for your reasons and accomplish very little except getting a belt rank.
Awesome that you try some Judo. Judo is frustrating as well as bjj. Try to avoid pulling guard and learn how to focus on breakinfalling correctly. Judo rules are different than bjj rules. Hang in there!
Thanks!
Most important is to start.